UH scientist joins Pluto protest

Petitioners ask an international astronomy organization for a better definition of planet

More than 300 astronomers, including University of Hawaii planetary scientist Dave Tholen, have signed a petition protesting the International Astronomical Union's new definition of a planet, which takes away Pluto's status as one of the main bodies in the solar system.

The astronomers do not necessarily oppose taking Pluto's planet status away, but they definitely do not like the new criteria for what is a planet.

Stern is principal investigator for the New Horizons spacecraft en route to what was the ninth planet -- Pluto -- until the IAU action.

"They have more votes protesting the decision than the people who voted for it," quipped Tholen, internationally renowned for his work on asteroids.

Says the petition, "We, as planetary scientists and astronomers, do not agree with the IAU's definition of a planet, nor will we use it. A better definition is needed."

Experts in all fields of astronomy, including international award-winning researchers, signed the petition.

A change cannot be made until the IAU's next General Assembly in three years, Tholen said.

"In the meantime, the IAU definition will stand as a source of confusion and incongruity to educators and the public," the petition's sponsors said in a news release. "An alternative is needed."

They plan to establish an open process allowing astronomers and planetary scientists to reach a consensus on "the issue of planets in our own solar system and elsewhere."

The IAU adopted a resolution defining a planet as an object that orbits the sun; is large enough for its own gravity to pull it into a round shape; and "has cleared the neighborhood around its orbit."

That knocked Pluto out of the planet family because it is located in the Kuiper Belt, a ring of debris with millions of cometlike remnants from the solar system's formation.

About 3,000 astronomers attended the IAU meetings Aug. 14-25 in Prague, Czech Republic, said Tholen, who was there with other Hawaii astronomers. But only those who were at the general assembly were eligible to vote, he said, estimating maybe 500 showed up.

"This is about as big a brouhaha in the astronomical world as I can recall," he said in an interview. "It's one of the most passionate discussions I've witnessed."

He said he voted against the resolution, "primarily because it's too difficult to apply to a newly discovered object. It requires too much information. ... I felt we needed something simpler."

He said he would not be surprised if the Pan STARRS survey, starting with a prototype telescope on Haleakala, finds a new object in the distant solar system.

It could be decades to answer the "scientifically rigorous" question of whether it is a planet under the new IAU definition, he said.

Tholen agrees with Institute for Astronomy colleague David Jewitt, discoverer of the Kuiper Belt with Jane Luu, that it makes no difference to science whether Pluto is called a planet.

After IAU's action, Jewitt said the astronomy association "did the right thing." In an e-mail during the controversy, he cited nostalgia and politics as reasons to classify Pluto as a planet. But he said, "Calling Pluto a planet opens a Pandora's box of planets that clouds the real significance of the many and varied types of bodies we find in the solar system."

Tholen asked, "Who is the definition for, the astronomers or the public?" His answer is it is really for the public because "Pluto is the same today as it was two years ago. It makes no different to astronomers. ... The biggest change is the way the public views the solar system."

He said he prefers an easy-to-apply definition. He feels the one the IAU chose is more complex than one originally proposed that was based on a concept of roundness.

The final version incorporates the roundness issue and also specifies that to be a planet, matter must be cleared out of the object's part of the solar system, he said.

For example, Ceres is the largest body in the asteroid belt, but it has a lot of company, so it has not cleared out its part of the solar system, Tholen said.

Still other issues are pending, he said. One concerns jurisdiction for naming 2003 UB313, a dwarf planet under the new definition that is comparable to or slightly larger than Pluto.

One committee deals with planets and satellites; another deals with comets and asteroids. "We want to get UB313 named. We don't know which is the right committee," Tholen said, suggesting getting both committees together to come up with a name.